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EUROPEAN ORGANIZATION FOR NUCLEAR RESEARCH

CERN-SPSC-2012-015SPSC-SR-101March 30, 2012

cloud2011 PROGRESS REPORT ON PS215/CLOUD

CLOUD Collaboration1 FIRST RESULTS

The first physics results from CLOUD [1] were published in Nature, August 2011 [2]. The measurementsrepresent the most rigorous laboratory evaluation yet accomplished of binary, ternary and ion-inducednucleation of sulphuric acid/ammonia aerosol particles under atmospheric conditions. Several new find-ings were reported. Firstly, CLOUD has shown that the most likely nucleating vapours, sulphuric acidand ammonia, cannot account for nucleation in the lower atmosphere. The nucleation observed in thechamber occurs at only one-tenth to one-thousandth of the rate observed in the lower atmosphere (Fig. 1).In view of the CLOUD results, the treatment of aerosol formation in climate models will need to be sub-stantially revised since all models assume that nucleation is caused by these vapours and water alone.Secondly, CLOUD has found that cosmic ray ionisation can substantially enhance nucleation of sul-phuric acid/ammonia particles—by up to a factor of 10. Ion-enhancement is particularly pronounced inthe cool temperatures of the mid-troposphere and above, where CLOUD has found that sulphuric acidand water vapour can nucleate without the need for additional vapours.

10-3

10-2

10-1

100

101

102

103

104

Nuc

leat

ion

rate

, J (c

m-3

s-1

)

105 106 107 108 109

Sulphuric acid concentration, [H2SO4] (cm-3)

CLOUD Jgcr 278 K, NH3 = 150 pptv 278 K, NH3 < 35 pptv 292 K, NH3 = 190 pptv 292 K, NH3 < 35 pptv

atmosphericobservations CLOUD

Fig. 1: Comparison of the nucleation rate of new particles as a function of [H2SO4] measured by CLOUD (largered and green circle symbols) with atmospheric boundary layer observations (small dot and circle symbols) [2].The measurements at 278 K and 292 K bracket the typical range of boundary layer temperatures.

Fig. 2: View of CLOUD in the East Hall T11 zone during the June-July 2011 run to study neutral and ion-inducednucleation involving organic vapours.

2 CLOUD RUNS

There were two physics runs for CLOUD in 2011, with the following aims:

CLOUD4: June - July 2011: Neutral and ion-induced ternary nucleation involving organic vapours(dimethylamine and pinanediol, a precursor of oxidised organic species from the important biogenicvapour, alpha-pinene). The CLOUD experimental configuration in the T11 zone during the June-Julyrun is shown in Fig.2.

CLOUD5: October - November 2011: Neutral and ion-induced binary (H2SO4−H2O) and ternary(NH3−H2SO4−H2O) nucleation over the entire tropospheric temperature range (to -65C).

3 CLOUD DETECTOR

Upgrades of the CLOUD facility in 2011 included:

• Completion of the thermal housing and precision thermo-regulation system (to -65C).

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• Cold racks (to -25C) for the sampling instruments.

• Completion of the final manhole covers and magnetic mixing fans.

• UV sabre for a) rapid aerosol growth and b) suppression of organic contaminants.

• Gas system upgrades for precision supply of organic vapours with low saturation vapour pressures.

• Commissioning of synthetic ultrapure water system.

4 PUBLICATIONS

The publication of the first CLOUD results in Nature [2] attracted wide interest in the media and scientificpress, including articles in The Economist [3], Wall Street Journal, CERN Courier [4], Nature News, andNature Geoscience [5]. The results were also reported at numerous scientific meetings, including aninvited plenary talk at the European Aerosol Conference, EAC2011, Manchester, September 2011.

The CLOUD4 and CLOUD5 runs in 2011 have revealed a number of important new findingswhich are currently being analysed. Several high profile (Nature/Science) manuscripts are in prepara-tion. At least two of these will be submitted for publication before 31 July 2012. This date marks thesubmission deadline for papers to be eligible for inclusion in the 5th Assessment Report (AR5) of theIntergovernmental Panel on Climate Change (IPCC), which is due to be completed by the end of 2013.For the first time, a chapter in AR5 will be devoted to “Clouds and Aerosols”, and it will contain a sectionon the influence of galactic cosmic rays.

In addition to the high profile manuscripts, a further 20 papers are in preparation for submissionto Atmospheric Chemistry and Physics, an open access—and highly popular—Journal of the EuropeanGeosciences Union. Several papers have already been published [6, 7, 8, 9] and about ten more areexpected to be submitted by mid 2012. Fourteen CLOUD abstracts have been submitted to the EuropeanAerosol Conference, EAC2012, Granada, September 2012.

5 COLLABORATION

Several new partners joined CLOUD during 2011, with special expertise as indicated:

Karlsruhe Institute of Technology, Germany: laboratory measurements of aerosols, liquid- and iceclouds (AIDA facility).

University of Stockholm, Sweden: atmospheric aerosol growth from organic vapours.

Carnegie Mellon University, USA: atmospheric organic chemistry and aerosol growth.

The Memorandum of Understanding for the maintenance and operation of CLOUD has been fi-nalised and signed by the CERN Director for Research and Computing. It is currently being signed bythe 19 CLOUD partners (U Innsbruck, U Vienna, U Helsinki, Finnish Meteorological Institute, U EasternFinland, U Frankfurt, Karslruhe Institute of Technology, Institute for Tropospheric Research - Leipzig,U Lisbon, Lebedev Physical Institute - Moscow, U Stockholm, CERN, PSI, U Leeds, U Manchester,Caltech, Carnegie Mellon, Aerodyne Research - Billerica and TOFWERK - Thun).

During 2011, CLOUD Collaboration meetings and data workshops were held at the University ofVienna, 14–18 February and Goethe University of Frankfurt, 25–30 September.

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6 PHYSICS AIMS AND BEAM REQUEST 2012

The beam requests and experimental aims for 2012 are as follows:

CLOUD6: 4 June - 2 July 2012 (4 weeks): Commissioning of the adiabatic expansion system tooperate CLOUD in a classical Wilson expansion chamber mode for generation of liquid and ice clouds.Instruments will be attached to CLOUD to measure, for the first time, the formation of liquid dropletsand ice particles inside the chamber. The purpose of this run is to prepare for future studies of the socalled “near-cloud” mechanism by which cosmic rays may directly influence cloud microphysics ratherthan through the production of cloud condensation nuclei (Fig. 3) [10]. Three spills per supercycle arerequested.

CLOUD7: 1 October - 3 December 2012 (9 weeks): Ion-induced and neutral nucleation and growthof sulphuric acid particles in the presence of oxidised organic vapours from pinanediol and alpha-pinene(Fig. 4). This represents a follow-up investigation of the new processes discovered during the CLOUD4run, and a new study of aerosol growth up to the size of cloud condensation nuclei (CCN). Three spillsper supercycle are requested.

galacticcosmicrays

ionisation

+++++++- - - -- - -

ionosphere>80 km altitude

fair weather currentJ ~ 2 pA m-2

(varies with GCR ionisation& thunderstorm generators)

+250 kV

0 V

200 Ω

1250 A

thunderstorm generators(40 lightning flashes s-1)

low cloud conductivity=> charge builds upon upper & lower edges

Fig. 3: The ion-aerosol “near-cloud” mechanism [10]. Highly charged aerosol particles develop at cloud bound-aries due to the build-up of space charge from the fair weather current. These charged aerosol particles may thenbecome entrained by clouds and possibly enhance the formation of ice particles.

cloud condensationnucleus (CCN)

(>50 nm)

cloud droplet (10-20 µm)

condensation

evaporation

condensation growth activation

condensationcoagulation

scavenging bypre-existing

aerosol (loss)

critical cluster(1.5 nm)

molecules

aerosol

1. Nucleation 2. Growth 3. Activation

Fig. 4: Aerosol nucleation and growth to cloud condensation nuclei (CCN). Around half of global CCN arethought to originate from this process but many aspects are poorly understood, including the participating vapours,nucleation rates, growth rates at different aerosol sizes, and effect on these processes of ionisation from galacticcosmic rays.

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fibre-optic UV system

temperature system

gassystem

air return duct

clearing field electrode

UVsabre

mixing fan

thermalhousing

pressure control& fast expansion

precisionthermo-regulator

air/H2O

SO2O3

trace gases

heatexchanger

circulationfan

3m CLOUDchamber

UV sensor

HV-

analysinginstruments

ice/dropletdetectors

HV+

3.5 GeV/c π+

beam hodoscope

Pt100

samplingprobes

heatexchanger

Fig. 5: Schematic of the CLOUD experiment in 2012.

7 FUTURE PLANS

CLOUD (Fig. 5) is tackling one of the most challenging problems in atmospheric science—to understandhow new aerosol particles are formed and grow in the atmosphere, and the effect these particles have onthe global atmosphere and climate. CLOUD also aims to answer definitively the question of whether ornot galactic cosmic rays affect clouds and climate, either by affecting aerosols or by directly influencingthe microphysics of liquid or ice clouds. The contribution of aerosols and clouds is recognised by theIntergovernmental Panel on Climate Change as the most important source of uncertainty in the radiativeforcing of climate change.

The present poor experimental understanding of aerosol nucleation and growth is preventing theinclusion of physics-based mechanisms in global models, and limiting our understanding of how a majorfraction of atmospheric aerosol will influence future climate. Development of reliable atmospheric mod-els requires quantifying the fundamental physics and chemistry of nucleation in the laboratory, as wellas a clear connection between the laboratory and the real world through these models.

In the near-term, the 2012 scientific goals for CLOUD are well-defined. During the 2013 shutdownof the CERN accelerators for the LHC energy upgrade, the CLOUD collaboration will likely devote amajor effort into analysis of the large quantity of high quality data already collected during the last 3years. Nevertheless, depending on the results obtained later in 2012, it is likely that CLOUD will operateat some stage during 2013 for special physics measurements that do not require a particle beam. Weexpect to begin normal data-taking operations for CLOUD when the PS beams return in 2014. Theprecise physics programme cannot be defined at this stage since it will depend on our findings during2012–2103.

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For the first time we have with the CLOUD facility at CERN an experimental chamber of the high-est technological performance which has established itself as the world’s leading experiment for thesestudies. CLOUD has also brought together a world-class team of atmospheric and modeling experts toconduct the experiments, analyse and interpret the data, and assess the impact of the results with globalmodels. Nevertheless, a multi-parameter experimental phase space must be mapped, involving numerousvariables such as temperature, relative humidity, trace gases and their concentrations, ionisation, nucle-ation rates, growth rates, droplet and ice particle activation, as well as liquid and ice cloud microphysics.CLOUD has been in operation for just over two years and we estimate around ten more years will berequired to carry out the experimental programme.

The projected CLOUD experimental programme is therefore likely to extend well beyond theplanned upgrade of the East Hall beamlines. After several year’s experience in the T11 beamline wewould like to request that T11 be retained for CLOUD in the new East Hall beamline layout, ideally with1–2 m additional space in the experimental zone in the direction towards T10. A dedicated T11 beam-line for CLOUD will maximise the efficiency and output of the experiment, and provide the maximumavailability of the T9 and T10 beamlines for test-beam users.

Acknowledgements

We would like to thank CERN PH-DT, EN-MME, EN-MEF and TE-VSC for their excellent support ofCLOUD and, in addition, to thank the CERN PS machine team and the PS Coordinator for their strongsupport of CLOUD and for efficient operation of the PS.

References

[1] CLOUD Collaboration: A study of the link between cosmic rays and clouds with a cloud chamberat the CERN PS.CERN-SPSC-2000-021 (2000), <http://cdsweb.cern.ch/record/444592>CERN-SPSC-2000-030 (2000), <http://cdsweb.cern.ch/record/462623>CERN-SPSC-2000-041 (2000), <http://cdsweb.cern.ch/record/497173>CERN-SPSC-2006-004 (2006). <http://cdsweb.cern.ch/record/923140>

[2] Kirkby, J., et al. Role of sulphuric acid, ammonia and galactic cosmic rays in atmospheric aerosolnucleation. Nature 476, 429–433 (2011).<http://www.nature.com/nature/journal/v476/n7361/full/nature10343.html>

[3] The Economist. Clouds in a jar; a new experiment with old apparatus reveals a flaw in models ofthe climate (27 August 2011). <http://www.economist.com/node/21526788>

[4] Kirkby, J. CLOUD: closing in on the initial steps of cloud formation. CERN Courier 51, 8, 28–31(October 2011). <http://cerncourier.com/cws/article/cern/47208>

[5] Pierce, J. Particulars of particle formation. Nature Geoscience 4, 665–666 (2011).<http://www.nature.com/ngeo/journal/v4/n10/full/ngeo1267.html>

[6] Kupc, A., et al.. A fibre-optic UV system for H2SO4 production in aerosol chambers causingminimal thermal effects. J. Aerosol Sci. 42, 8, 532–543 (2011).

[7] Voigtlander, J., Duplissy, J., & Stratmann, F. Numerical simulation of flow, H2SO4 cycle and newparticle formation in the CERN CLOUD chamber. Atmos. Chem. Phys. Discuss. 11, 20013–20049(2011).

[8] Bianchi, F., Dommen, J., Mathot, S., & Baltensperger, U. On-line determination of ammonia at lowpptv mixing ratios in the CLOUD chamber. Atmos. Chem. Phys. Discuss. 5, 2111–2130 (2012).

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[9] Praplan, A.P., Bianchi, F., Dommen, J., & Baltensperger, U. Dimethylamine and ammonia mea-surements with ion chromatography during the CLOUD4 campaign. Atmos. Chem. Phys. Discuss.5, 2395–2413 (2012).

[10] Carslaw, K.S., Harrison, R.G., & Kirkby, J. Cosmic rays, clouds, and climate. Science 298, 1732–1737 (2002).

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